Examples
Foobar Player Audio Processing
This is a great method to use if you only need crossovers, EQ and delay for music. If it needs to work for anything else, such as video, skip this method. All the processing is done by the player itself.

Sound Blaster with KXProject Drivers Audio Processing
This is a good entry level point. It will do everything you need it to do in music and video since all the processing is done by the DSP chip on the soundcard itself. That means your computer processor does not need to do any processing. This is equivalent to the crossovers built into headunits, amplifiers, and outboard crossovers.

ASIO VST Plug-in Audio Tuning Method
If you want nothing but unlimited tuning capabilities this is the way to go. It is superior to any of the other methods based on the fact the plug-ins are more professional. It is very tricky to get this method to work and requires a good balance of the right hardware and software. The downside to this is that it is complex and requires all the processing to be performed by the CPU. You will need a minimum of a Pentium 4/AMD equivalent processor. There are a lot of little details you have to worry about if you pick this method.

VST Plugin method with Any soundcard and Console + Virtual Audio Cable
This will allow you to use all available VST plugins with any brand soundcard. It is limited however to MUSIC ONLY playback-no video.

VST plugin method with ASIO drivers and Reaper
Another alternative to signal routing and audio stream routing similar to using VAC. Details here.